This invention relates generally to electromagnetic locks which control the access through doors. More particularly, this invention relates to electromagnetic locks responsive to door motion for controlling egress or entrance through an associated doorway.
Electromagnetic door locks are well-known in the art not only for locking characteristics, but also as key components in systems which control the opening and closing of doors for security and safety sensitive areas. For many doorways, simple locked and unlocked states for a door are not sufficient for security and safety concerns. Time delays for the release of an electromagnetic lock have been employed to enhance the security of entrance and egress through a particular doorway. Dramatic improvements in safety and security have been provided by locks which are automatically responsive to a force applied to a door to initiate a delay interval on the order of 15 to 30 seconds before allowing the door to open. The time delay incorporated into a lock operation allows security or safety personnel time to investigate the circumstances of an attempted opening of a particular doorway before the lock automatically releases and the door actually opens.
Frolov et al U.S. Pat. No. 5,065,136, assigned to the assignee of the present invention, discloses an electromagnetic door security system responsive to an application of force to the door for which the lock has been installed. The electronic lock may automatically respond to an application of force to the door by either immediately sounding an alarm and releasing the lock or initiating a time delay sequence before the lock releases and allows the door to open. The delay in the release of an electromagnetic lock is employed to provide appropriate security or safety personnel time to respond to an unauthorized egress or entrance through a particular door. The lock may also immediately trigger an alarm system for the warning of either security or safety concerns.
Frolov et al U.S. Pat. No. 5,065,136 discloses an electromagnet which is mounted for rocking movement in a lock frame. The rocking mount is provided by a pair of coaxial pivot pins having an axis which is substantially coplanar with the door frame header on which the lock is mounted. An armature attractable to the electromagnet is mounted to the door. The electromagnet rests in a first position relative to the lock frame under the force of gravity. A force applied to the door and therefore the armature results in the electromagnet rocking to a second position relative to the frame. This rocking motion activates a switch in the lock to generate a signal. The activation signal may result in an instant release of the electromagnet, a time delayed release of the electromagnet, and/or triggering of an alarm system.